The present invention relates generally to a system for controlling the operation of a printer, and more particularly, to a system for controlling the operation of a printer when end of a piece of paper approaching the platen of the printer is first detected.
Conventional printers include paper detectors for determining when printable matter can be recorded on the paper. The detector provides two different outputs corresponding to the presence and absence of paper. When the trailing edge of the paper is detected by the paper detector, the detector's output changes to indicate the absence of paper. When the leading edge of the paper is detected by the paper detector, the detector's output changes to indicate the detected presence of the paper.
The detector is typically disposed behind a print head so that as the paper advances through the printer the paper passes by the paper detector before reaching the print head. When the absence of paper is first detected, that portion of the paper between the print head and paper detector (hereinafter referred to as an override amount L) remains to be advanced beyond the print head. To permit printing of printable matter on a override amount L, conventional printers continuously monitor the output of the paper detector for continuous indication of paper absence. Printing on override amount L continues until a maximum line count, corresponding to the maximum amount of printable matter, within override amount L is reached.
The printer considers that the next piece of paper is set for printing when the presence of paper is once again detected by the paper detector. When the next piece of paper is detected, print control action for the last piece of paper is terminated and ejection of the last piece of paper is initiated by the printer.
The paper detector generally includes either a microswitch or phototransistor. The microswitch is actuated by the weight of the paper. The phototransistor unit is actuated light is interrupted. The output of the paper detector tends to include chatter (i.e. noise) caused by the vibration of the paper, printer or surrounding conditions. Such chatter during printing of override amount L can be erroneously interpreted by the printer as representing the detected presence of paper. Printing of less than all of the printable matter within override amount L results. Undesirable variations in the bottom margin of each printed page also occurs.
Accordingly, it is desirable to provide a printer control device and method which maximizes the amount of printable matter recorded on a page by preventing the premature termination of recording printable matter within override amount L.